1. Technical Field
The present invention relates generally to computer systems and, in particular, to a computer system having low energy consumption.
2. Background Description
In recent years, pervasive devices (PvDs) have become increasingly popular. The wireless capabilities of these devices are increasing as well as the computational complexity required by certain tasks. A major obstacle to the success of pervasive devices is energy consumption, since pervasive devices are typically powered by batteries. In general, a battery in a pervasive device may last anywhere from one hour to one year depending on the use(s) of the pervasive device. If the pervasive device is used for speech recognition and/or to support high speed wireless connectivity, it is inevitable that the energy consumption will go up significantly. The reason for this is that moderate to high performance processing units are needed to support the Million Instructions Per Second (MIPS) required by such tasks. Unfortunately, as performance goes up, energy efficiency goes down. As used herein, the phrase “energy efficiency” is directed to joules-per-task (JPT) (and other equivalents).
Despite all the high performance and complex tasks that current pervasive devices are capable of performing, the majority of a typical pervasive device's life is spent doing simple low performance tasks such as updating the time register, periodically exchanging location information with wireless base station, sampling the ambient temperature, logging a GPS location stamp, fetching an address book entry, updating the screen buffer, detecting a keypad input, and so forth. Executing such simple tasks on a high performance processor is extremely inefficient in terms of JPT.
Thus, there have been a number of attempts to run processing units in a energy conscious manner. For example, some processor manufacturers (see, e.g., T. R. Halfhill, “Transmeta Breaks x86 Low-Power Barrier”, Microprocessor Report, p. 1, February 2000; and S. Liebson, “Xscale (StrongARM-2) Muscles In”, Microprocessor Report, p. 1, February 2000) have produced more energy efficient processing units wherein the energy consumption per cycle can be adjusted by changing supply voltage and frequency in tandem, also known as voltage scaling (see, e.g., Brodersen et al., “Low Power Digital CMOS Design”, Kluwer Academic Publishers, 1995). However, there are limits to how slow these processing units can be made to run or, rather, to how low the supply voltage can be driven. Therefore, if these processing units are primarily used to execute simple low performance tasks, then they would still dissipate significantly more energy than processing units specifically designed to execute such simple tasks.
“Further, some mobile telephone and portable radio manufacturers (see, e.g., U.S. Pat. No. 5,487,181, issued on Jan. 23, 1996, assigned to Ericsson GE Mobile Communications Inc., Lynchburg, Va., the disclosure of which is incorporated herein by reference; and U.S. Pat. No. 5,058,203, issued on Oct. 15, 1991, assigned to Fujitsu Limited, Kawasaki, Japan, the disclosure of which is incorporated herein by reference) have proposed to use energy efficient application specific integrated circuits (ASIC) to offload the less energy efficient main processor in performing frequently occurring and routine functions. However, this approach for reducing energy consumption is not suitable for a more generic and more configurable computing platform which is intended to offer a high degree of flexibility to the user. In a highly flexible computing system, the user may change functionality and install new features on the fly (e.g., the desktop user paradigm). The proposed conventional solutions are not flexible systems. Rather, they are systems with specific and limited functionality.
Accordingly, there is still a need for a generic configurable computing platform having low energy consumption irrespective of system functionality demands by users, which can download new application code for evaluation and subsequent execution in the most energy efficient manner.